JP2010082198A - Ultrasonic signal processing apparatus and method - Google Patents

Abstract

Information indicating speckle-likeness or non-speckle-likeness is obtained accurately and easily.
An ultrasonic probe that transmits an ultrasonic wave toward a subject, receives an ultrasonic echo from within the subject, and generates a reception signal indicating the ultrasonic echo; and A signal processing unit 24 and a phase difference image generation unit 28 that acquire a plurality of phase differences respectively corresponding to the frequencies of the ultrasonic waves from the received signal, and a ratio between a plurality of the frequency ratios and a plurality of the phase difference ratios. A speckle index calculation unit 30 for calculating a corresponding speckle index is provided.
[Selection] Figure 5

Description

  The present invention relates to an ultrasonic signal processing apparatus and method capable of accurately and easily obtaining information indicating speckle-likeness or non-speckle-likeness.

  2. Description of the Related Art There is known an ultrasonic signal processing apparatus that transmits ultrasonic waves toward a subject, receives ultrasonic echoes from the subject, and displays an ultrasonic image generated based on a received signal.

  For example, since the time (propagation time) from transmitting an ultrasonic wave to receiving an ultrasonic echo varies depending on the depth of the reflection position in the subject, the propagation time is associated with the depth of the reflection position in the subject. At the same time, an amplitude image of the B mode is generated by associating the amplitude of the received signal with the luminance.

  By the way, speckle noise (sometimes simply referred to as “speckle”) is generated due to random interference of reflected waves in the subject.

  Conventionally, speckle reduction technology uses multiple smoothing filters, adaptively changes according to the image structure, multi-resolution decomposition, morphological processing, etc. Focus on the image structure and apply the filter to a single frame image There is technology to do.

Patent Document 1 discloses a configuration in which noise is reduced by synthesizing a plurality of reception signals in which a positional relationship with a subject is matched in a compound scanning type.
JP 2003-70786 A

  There is a problem that it is difficult to accurately and easily obtain information indicating speckle-likeness or non-speckle-likeness.

  For example, when image structures are very similar between tissue boundaries or isolated points and speckle noise, it is difficult to separate speckle noise from non-speckle signals.

  Even in the technique of reducing speckle by weighted averaging in multiple frames, taking advantage of the fact that the change in speckle noise between frames is larger than the change in non-speckle signals, non-speckle signals are similar to speckle noise. Since the frame changes like this, separation is difficult.

  In short, the speckle reduction technique described in Patent Document 1 focuses on the fact that in an image obtained from a multi-directional beam, the speckle image changes because the interference situation changes, but the non-speckle signal does not change. ing. However, the difference is not clear and may be difficult to separate.

  If information indicating speckle-like or non-speckle-like information can be obtained accurately and easily, not only speckle noise and non-speckle signals are separated, but also speckle noise removal, speckle tracking, organizational properties. Various processes such as analysis and non-speckle partial emphasis can be performed accurately and easily.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an ultrasonic signal processing apparatus and method capable of accurately and easily obtaining information indicating speckle-likeness or non-speckle-likeness. .

  In order to achieve the object, the present invention transmits an ultrasonic wave toward a subject, receives an ultrasonic echo from within the subject, and generates a reception signal indicating the ultrasonic echo. Corresponding to the size of a plurality of phase difference acquisition means, a phase difference acquisition means for acquiring a plurality of phase differences respectively corresponding to the frequencies of the ultrasonic waves from the received signal, and a ratio of a plurality of the frequency ratios and a plurality of the phase difference ratios There is provided an ultrasonic signal processing device comprising: speckle index calculating means for calculating a speckle index.

  According to this, by utilizing the fact that the phase change of the non-speckle signal is proportional to the ultrasonic frequency, it is possible to accurately and easily obtain information (speckle index) indicating speckle-likeness or non-speckle-likeness. it can.

  As one aspect of the present invention, the speckle index calculating means corrects the phase difference by multiplying the phase difference by a ratio between the frequencies, and compares the phase difference after the correction to perform the comparison. The index is calculated. According to this, since the speckle index is calculated by comparing with the phase difference after correction, which is a result of multiplying the phase difference by the ratio between the frequencies, for example, when generating a high-resolution ultrasonic image In addition, it is possible to easily calculate a speckle index for each pixel with high resolution.

  Further, the speckle index calculating means integrates the absolute value of the phase difference after correction in a fixed size space including each spatial position, thereby calculating the speckle index for each spatial position. It is preferable to calculate. For example, in the phase difference image indicating the phase difference, each pixel is integrated by integrating the absolute value of the phase difference after the correction with a constant volume (or a constant area or a constant length) around each pixel. Calculate the speckle index for each.

  According to this, for example, when generating a high-resolution ultrasonic image, it is possible to calculate a speckle index that accurately indicates speckle-likeness or non-speckle-likeness for each pixel.

  There are various modes for acquiring a plurality of types of phase differences respectively corresponding to a plurality of ultrasonic frequencies.

  For example, ultrasonic waves having different frequencies are transmitted from the ultrasonic transmission / reception means.

  Further, for example, an ultrasonic wave having a plurality of frequency bands is transmitted from the ultrasonic wave transmitting / receiving means, and the received signal is divided into bands.

  Further, for example, a fundamental wave is transmitted from the ultrasonic wave transmitting / receiving means, and a fundamental wave component and a harmonic component are extracted from the received signal based on a difference in band.

  Further, it is preferable that the speckle index calculation unit uses data in which the phase resolution in the element arrangement direction of the ultrasonic transmission / reception unit is equal to or greater than the interval between the elements.

  Further, the ultrasonic transmission / reception means can generate the reception data of two or more sound rays in the arrangement direction of the elements of the ultrasonic transmission means by one ultrasonic transmission, the speckle index calculation means, It is preferable to use the reception data of two or more sound lines generated by the ultrasonic transmission / reception means.

  There are various ways of using the speckle index.

  For example, using the speckle information, separation of non-speckle signals and speckle noise, removal of speckle noise, speckle tracking, tissue property analysis, or non-speckle partial enhancement is performed.

  Further, for example, an image reflecting the speckle index is displayed on the display means.

  The image reflecting the speckle index and the amplitude image indicating the spatial amplitude of the received signal may be combined and displayed on the display means.

  An amplitude image indicating the spatial amplitude of the received signal may be modulated by the speckle index and displayed on the display means.

  You may provide the mode switching means which switches the mode which displays the image in which the said speckle index was reflected, and the mode which does not display the image in which the said speckle index was reflected. In addition, the present invention transmits an ultrasonic wave toward the subject, receives an ultrasonic echo from within the subject, generates a reception signal indicating the ultrasonic echo, and generates the reception signal from the reception signal. Ultrasonic signal processing characterized in that a plurality of phase differences respectively corresponding to sound wave frequencies are acquired, and a speckle index corresponding to the magnitude of a ratio of the plurality of frequencies and a plurality of phase difference ratios is calculated. Provide a method.

  According to the present invention, information indicating speckle-likeness or non-speckle-likeness can be obtained accurately and easily.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<Principle of the present invention>
First, the principle of the present invention will be described.

  In FIG. 1, the ultrasonic probe 20 transmits an ultrasonic wave toward the subject 90 and receives a reflected wave (hereinafter referred to as “ultrasonic echo”) from within the subject 90 to receive the ultrasonic wave. A plurality of ultrasonic transmitting / receiving elements that generate reception signals indicating echoes are arranged.

  Hereinafter, the direction x (element arrangement direction) in which the ultrasonic transmission / reception elements are arranged may be referred to as “azimuth direction” (or “scan direction”). In addition, the depth direction y of the subject 90 may be referred to as a “distance direction”. In addition, the direction z orthogonal to both the depth direction and the element array direction, that is, the direction z orthogonal to the tomographic plane may be referred to as “slice direction” (or “frame direction”).

  For convenience of explanation, the ultrasonic probe 20 having one-dimensionally arranged ultrasonic transmission / reception elements will be described as an example, but the present invention can also be applied to a case where the ultrasonic transmission / reception elements are two-dimensionally arranged. . Further, the present invention is not limited to the case where the ultrasonic transmission / reception elements are arranged in a planar shape, but can be applied to the case where the ultrasonic transmission / reception elements are arranged in an arbitrary curved shape.

  Next, the relationship between the generation of speckle noise, the ultrasonic frequency, and the phase difference between ultrasonic echoes will be described.

  FIG. 2 (a) shows a non-speckle wave 201 and a speckle wave 202 in the subject at the first ultrasonic frequency f0, and the inside of the subject at the second ultrasonic frequency (2 × f0 in this example). A non-speckle wave 211 and a speckle wave 212 are schematically shown. Here, the non-speckle waves 201 and 211 are ultrasonic waves (normal reflected waves) reflected at a reflection point in the subject. The speckle waves 202 and 212 are interference waves generated by interference due to innumerable scattering. In fact, non-speckle waves and speckle waves are mixed in the received waves received as ultrasonic echoes by the ultrasonic probe 20.

  FIG. 2B shows a correspondence relationship between the ultrasonic frequency (f0, 2 × f0) and the phase difference (spatial phase difference and temporal phase difference) in the non-speckle signal. FIG. 2C shows the correspondence between the ultrasonic frequency (f0, 2 × f0) in speckle noise and the phase difference. Here, the non-speckle signal and the speckle noise are components corresponding to the non-speckle wave and the speckle wave, respectively, in the received signal.

  In the non-speckle signal, as shown in FIG. 2B, when the ultrasonic frequency is doubled, the phase difference is also doubled. In this way, a proportional relationship is established between the ultrasonic frequency and the phase difference. Such a proportional relationship is kept constant in each direction (distance direction, azimuth direction, slice direction) of the spatial region. In the non-speckle signal, as shown in FIG. 2B, if the ultrasonic frequency is constant, the spatial phase difference is kept constant in each direction of the spatial region.

  On the other hand, since speckle noise is a result of interference due to innumerable scattering, the interference state changes according to the ultrasonic frequency. As shown in FIG. 2C, the spatial phase difference changes in each direction (distance direction, azimuth direction, slice direction) of the spatial region.

  Next, a method for obtaining a speckle index indicating speckle-likeness or non-speckle-likeness using two different ultrasonic frequencies f0 and f1 will be described.

  In the non-speckle signal, since the phase difference is proportional to the ultrasonic frequency, logically, the ratio (f1 / f0) between the first ultrasonic frequency f0 and the second ultrasonic frequency f1 and the first The ratio (Δφ1 / Δφ0) between the phase difference Δφ0 corresponding to the ultrasonic frequency f0 and the phase difference Δφ1 corresponding to the second ultrasonic frequency f1 satisfies Equation 1.

[Equation 1]
f1 / f0−Δφ1 / Δφ0 = 0
However, in actuality, since non-speckle signals and speckle noise are mixed, the speckle index indicating the likelihood of speckle noise (or the likelihood of non-speckle signal), not whether or not the equation 1 is satisfied. Is derived.

  For example, the speckle index Si is obtained as shown in Equation 2.

[Equation 2]
Si = | Δφ0 × (f1 / f0) −Δφ1 |
Here, the speckle index Si indicates that the larger the value is, the more speckle noise is, and the closer the value is to 0, the more likely it is a non-speckle signal.

  Multiplying the right side of Equation 2 by (fr / f1) yields Equation 3.

[Equation 3]
Si = | Δφ0 × (fr / f0) −Δφ1 × (fr / f1) |
Here, fr is a specific frequency for normalizing the phase difference.

  That is, by multiplying the phase difference by the ratio between the frequencies, the phase difference is corrected to normalize to a specific frequency fr, and the corrected phase differences (phase differences normalized to fr) are compared with each other. By doing so, the speckle index Si can be easily calculated.

  By using such speckle index Si for separation of speckle noise and non-speckle signal, removal of speckle noise, speckle tracking (tracking), tissue characterization, non-speckle partial enhancement, etc. Appropriate diagnosis is possible.

  For example, the speckle index Si is obtained for each spatial position corresponding to each reflection point of ultrasonic waves. For example, the speckle index Si is obtained for each pixel position of the ultrasonic image generated from the received signal.

  Here, it is preferable to integrate with a kernel of a certain size. In this case, the speckle index Si is expressed by Equation 4.

[Equation 4]
Si = Σ | Δφ0 × (fr / f0) −Δφ1 × (fr / f1) |
Here, the symbol “Σ” indicates that integration (summation) is performed at a constant volume, a constant area, or a constant length.

  For example, as shown in FIG. 3, a three-dimensional phase difference image 300 (a two-dimensional phase difference image 302 is arranged in the slice direction z) corresponding to the subject 90 is generated for each fixed volume 304. Then, the absolute value of the spatial phase difference after correction is integrated. In this way, an accurate speckle index can be obtained by integrating in three dimensions, but for simple integration, two-dimensional integration is performed for each fixed area in the two-dimensional phase difference image 302. Alternatively, one-dimensional integration may be performed for every fixed length.

  Note that Si is expressed by Equation 5 when fr = f1 in Equation 4, and is expressed by Equation 6 when fr = 1.

[Equation 5]
Si = Σ | Δφ0 × (f1 / f0) −Δφ1 |
[Equation 6]
Si = Σ | Δφ0 / f0−Δφ1 / f1) |
In any case of Equations 4 to 6, it can be said that the phase difference is corrected by multiplying the phase difference by the ratio of the ultrasonic frequency. Instead of the speckle index Si shown in Equations 4 to 6, the absolute value (| f1 / f0−Δφ1 / Δφ0 |) of the difference between the ratio between the frequencies and the ratio between the corresponding phase differences is integrated. You may do it. The former is an index that integrates the difference of the distance difference corresponding to the spatial phase difference for each frequency, and the latter is an index that integrates the value obtained by subtracting the ratio of the distance difference corresponding to the spatial phase difference for each frequency from 1. In both cases, the smaller the distance difference for each frequency, the closer to 0.

  FIG. 4 is a flowchart showing an outline of processing for obtaining the speckle index Si.

  In step S1, a plurality of types of phase differences respectively corresponding to a plurality of ultrasonic frequencies are acquired from the received signal. Although a temporal phase difference is detected in the distance direction, it may be regarded as a spatial phase difference as it is, or may be converted into a spatial phase difference using an assumed sound speed.

  For example, first, an ultrasonic wave having the first frequency f0 is transmitted, and the phase difference Δφ0 is acquired from the reception signal of the ultrasonic echo. Next, an ultrasonic wave having the second frequency f1 is transmitted, and the phase difference Δφ1 is acquired from the received signal of the ultrasonic echo.

  In step S2, the speckle index is calculated by Equation 5, for example. Thereby, the speckle index corresponding to the magnitude of the ratio of the plurality of frequencies and the ratio of the plurality of phase differences is calculated.

  In addition, although the case where the numerical value (speckle index) was calculated as an example of the speckle index indicating speckle-likeness or non-speckle-likeness was described, the speckle index is not particularly limited to the numerical value in the present invention, Any type of information (eg, image, character string) may be used.

<Ultrasonic image processing device>
FIG. 5 is a block diagram illustrating a configuration example of an ultrasonic image processing apparatus including the ultrasonic signal processing apparatus according to the present invention.

  In FIG. 5, the ultrasonic image processing apparatus 10 mainly includes an operation unit 12, a display unit 14, an ultrasonic probe 20, a transmission / reception unit 22, a time domain signal processing unit 24, an amplitude image generation unit 26 (spatial amplitude). Acquisition means), a phase difference image generation unit 28 (spatial phase difference acquisition means), a speckle index calculation unit 30, an image processing unit 40, a display control unit 42, and a mode switching unit 44.

  The operation unit 12 is an instruction input device for inputting a user instruction. For example, it is composed of a keyboard, a mouse and the like.

  The display unit 14 is a display device that can display an image. For example, it is configured by an LCD (liquid crystal display) or the like.

  The ultrasonic probe 20 transmits ultrasonic waves toward the subject and receives ultrasonic echoes reflected in the subject. The ultrasonic probe 20 includes, for example, a plurality of ultrasonic transducers constituting a one-dimensional ultrasonic transducer array (linear array probe), and each ultrasonic transducer has electrodes at both ends of a piezoelectric element such as PZT. It is comprised by the vibrator | oscillator which formed.

  In addition to a linear array probe in which a plurality of ultrasonic transducers are arranged one-dimensionally, a sector probe that scans the inside of a subject in a fan shape, a convex array probe in which a plurality of ultrasonic transducers are arranged on a convex surface, or A two-dimensional array probe in which a plurality of ultrasonic transducers are two-dimensionally arranged may be used. Alternatively, a mechanical radial probe that performs radial scanning in an ultrasonic endoscope may be used.

  The transmission / reception unit 22 gives an ultrasonic transmission signal to the ultrasonic probe 20 and causes the ultrasonic probe 20 to generate ultrasonic waves.

  The ultrasonic probe 20 transmits an ultrasonic beam into the subject by driving the transmitting / receiving unit 22 and scans the subject by a scanning method such as linear scanning, sector scanning, convex scanning, or radial scanning. To do. The ultrasonic wave generated by the ultrasonic probe 20 is reflected by a reflector existing in the body of the subject, and the ultrasonic echo is received by the ultrasonic probe 20. When the ultrasonic echo is received by the ultrasonic probe 20, the ultrasonic probe 20 outputs a reception signal indicating the ultrasonic echo, so that the transmission / reception unit 22 amplifies the received signal and performs A (analog). After / D (digital) conversion, receiving focus is applied and input to the time domain signal processing unit 24. With reception focus, reception data (sound ray data) of two or more sound rays in the element arrangement direction is generated by one ultrasonic transmission. For example, reception focus may be performed as described in Japanese Patent Application Laid-Open No. 2008-167985.

  The time domain signal processing unit 24 performs processing to acquire time domain amplitude information and time domain phase information from the received signal of the ultrasonic echo.

  The signal processing unit 24 of this example includes an orthogonal detection unit 241, an amplitude information calculation unit 242, and a phase information calculation unit 243.

  The quadrature detection unit 241 performs quadrature detection on the received signal of the ultrasonic echo indicating the ultrasonic echo.

  The received signal e (t) is expressed by the following equation.

[Equation 7]
e (t) = u (t) × cos (ωt + φ (t))
Here, u (t) indicates the amplitude, and φ (t) indicates the phase.

  The received signal e (t) is separated into a real component I (cos component) and an imaginary component Q (sin component) by quadrature detection, as shown in the following equation.

[Equation 8]
I = u (t) cos (φ (t))
Q = u (t) sin (φ (t))
The real component is also called I component and the imaginary component is also called Q component.

  The amplitude information calculation unit 242 calculates the amplitude u (t) by the following equation based on the I component and Q component obtained by the quadrature detection unit 241.

[Equation 9]
u (t) = √ (I ² + Q ² )
The phase information calculation unit 243 calculates the phase φ (t) by the following equation based on the I component and Q component obtained by the quadrature detection unit 241.

[Equation 10]
φ (t) = tan ^-1 I / Q
The quadrature detection unit 241 and the amplitude information calculation unit 242 constitute temporal amplitude acquisition means for acquiring u (t) as amplitude information in the time domain. Further, the quadrature detection unit 241 and the phase information calculation unit 243 constitute temporal phase acquisition means for acquiring φ (t) as phase information in the time domain.

  The amplitude image generation unit 26 associates the amplitude information u (t) in the time domain of each sound ray data with the position x in the azimuth direction, and uses the assumed sound velocity to detect amplitude information in the spatial domain of the tomographic plane (x, y). By converting to u (x, y), an amplitude image (for example, a B-mode amplitude image) indicating the amplitude of the ultrasonic echo from each reflection position in the subject is generated. As for the amplitude information in the spatial domain, the time from propagation of an ultrasonic pulse to reception of an ultrasonic echo pulse (propagation time) varies depending on the depth of the reflection position. It is calculated by associating with the depth of the reflection position in the subject and associating the amplitude value with the pixel value (indicating luminance or color).

  The phase difference image generation unit 28 associates the phase information φ (t) in the time domain of each sound ray data with the position x in the azimuth direction, and uses the assumed sound velocity in the spatial domain of the tomographic plane (x, y). By converting to information φ (x, y), and further converting to a phase difference Δφx (x, y) in the azimuth direction and a phase difference Δφy (x, y) in the distance direction, A phase difference image indicating the phase difference of the ultrasonic echo is generated. Specifically, since the time (propagation time) from the transmission of an ultrasonic pulse to the reception of an ultrasonic echo pulse varies depending on the depth of the reflection position, the propagation time is calculated using the assumed sound velocity. The phase difference image is generated by associating the value of the phase difference with the pixel value (indicating luminance or color). A plurality of phase images may be generated in the slice direction, and the spatial phase difference Δφz (x, y) in the slice direction may be generated. .

  Note that when speckle noise exists parallel to either the azimuth direction or the distance direction, the phase change is small in that direction, but the phase change is large in the direction orthogonal thereto, so the spatial phase difference Δφx in the azimuth direction. It is preferable to determine (x, y), the spatial phase difference Δφy (x, y) in the distance direction, and the spatial phase difference Δφz (x, y) in the slice direction. A two-dimensional spatial phase difference Δφxy (x, y) that is the square root of the square sum of Δφx (x, y) and Δφy (x, y) or a three-dimensional spatial phase difference Δφxyz (x, y) You may ask for it.

  Note that the spatial phase difference in the slice direction can be easily calculated if the ultrasonic probe 20 is a two-dimensional probe. In addition, even when the positional relationship in the slice direction is known even with a one-dimensional probe (for example, a probe with a magnetic sensor or an automatic scan function), the spatial phase difference in the slice direction can be easily calculated.

  The amplitude image generation unit 26 constitutes a spatial amplitude acquisition unit that acquires amplitude information in the spatial region. In addition, the phase difference image generation unit 28 constitutes a spatial phase difference acquisition unit that acquires phase difference information in the spatial domain.

  The speckle index calculation unit 30 calculates a speckle index. Specifically, the spatial phase difference is corrected by normalizing the spatial phase difference by multiplying the spatial phase difference by the ratio between the ultrasonic frequencies, and at a fixed volume, a fixed area, or a fixed length around each pixel. The speckle index for each pixel position is calculated by integrating the absolute value of the spatial phase difference after correction.

  When the speckle index is calculated by volume integration, phase differences such as Δφx, Δφy, and Δφz are held corresponding to the three-dimensional positions x, y, and z.

  The image processing unit 40 performs various types of image processing using the speckle index calculated by the speckle index calculation unit 30.

  The image processing of the image processing unit 40 includes processes such as separation of non-speckle signals and speckle noise, removal of speckle noise, speckle tracking, tissue property analysis, and non-speckle partial enhancement.

  In addition, the image processing of the image processing unit 40 includes an image reflecting a speckle index (for example, an image showing a non-speckle signal after separation, an image showing speckle noise after separation, and a speckle tracking result). Image, an image showing a tissue property analysis result, an image in which a non-speckle portion is emphasized) and an amplitude image are included. For example, the composition is performed by modulating with the luminance or color of the amplitude image by the image reflecting the speckle index.

  The image processing unit 40 has a function of combining the amplitude image and the phase difference image. For example, the composition is performed by modulating the luminance or color of the amplitude image by the phase difference image. The composition may be performed directly by modulating the luminance or color of the amplitude image with a speckle index.

  The display control unit 42 selects an arbitrary image according to an instruction from a mode switching unit 44 described later, performs enlargement / reduction processing and layout processing, and inputs the selected image to the display unit 14. There are various combinations of images to be displayed. For example, the image reflecting the speckle index and the amplitude image are arranged and displayed on the display unit 14. Only the amplitude image, only the image reflecting the speckle index, or only the composite image may be displayed.

  The mode switching unit 44 has a function of switching modes according to a user instruction input to the operation unit 12.

  For example, the mode switching unit 44 has a function of switching between a mode in which an image in which a speckle index is reflected and a mode in which an image in which a speckle index is reflected is not displayed.

  In this example, the resolution of the phase in the arrangement direction of the elements of the ultrasonic probe 20 is equal to or greater than the interval between the elements of the ultrasonic probe 20. That is, the resolution in the element arrangement direction of the phase difference image generated by the phase difference image generation unit 28 is preferably equal to or greater than the interval between elements of the ultrasonic probe 20 (for example, an ultrasonic transducer). As a result, the phase difference in the azimuth direction does not wrap around, and erroneous calculation of the speckle index can be prevented.

  The time domain signal processing unit 24, the amplitude image generation unit 26, the phase difference image generation unit 28, the speckle index calculation unit 30, the image processing unit 40, the display control unit 42, and the mode switching unit 44 are, for example, a CPU (Central Processing Unit). Unit). Some of these may be configured by a circuit.

  Although the case where the phase difference image is generated by the phase difference image generation unit 28 as information indicating the spatial phase difference corresponding to each reflection position in the subject has been described as an example, the present invention is a phase difference image. Is not particularly limited, and invisible information may be generated instead of a visible image. Similarly, the case where an amplitude image is generated by the amplitude image generation unit 26 as information indicating the spatial amplitude corresponding to each reflection position in the subject has been described as an example, but the present invention generates an amplitude image. In this case, there is no particular limitation, and invisible information may be generated instead of a visible image.

  FIG. 6 is a flowchart illustrating an exemplary flow of speckle index calculation processing. This processing includes the transmission / reception unit 22, the time domain signal processing unit 24, the amplitude image generation unit 26, the phase difference image generation unit 28, the speckle index calculation unit 30, the image processing unit 40, the display control unit 42, the mode switching unit 44, and the like. It is executed according to a program by a CPU (Central Processing Unit) constituting the.

  In step S11, the spatial phase difference Δφ0 is calculated from the RF data (reception signal) of the first frequency f0, and in step S12, the spatial phase difference Δφ1 is calculated from the RF data (reception signal) of the second frequency f1. Is calculated.

  There are various modes for obtaining RF data of different frequencies (f0, f1).

  First, there is an aspect in which the transmission / reception unit 22 transmits ultrasonic waves of the first frequency f1 and ultrasonic waves of the second frequency f1 from the ultrasonic probe 20, respectively. That is, ultrasonic waves having different frequencies are transmitted from the ultrasonic probe 20.

  Second, there is a mode in which the transmitter / receiver 22 transmits ultrasonic waves having a plurality of frequency bands from the ultrasonic probe 20 at a time. Further, the transmission / reception unit 22 divides the received signal into bands using a band filter or the like.

  Third, the transmission / reception unit 22 uses the transmission / reception unit 22 to separately extract the fundamental wave component and the harmonic component having different frequency bands from the received signal.

  In step S13, the speckle index calculation unit 30 multiplies the spatial phase difference Δφ0 at the first frequency f0 by f1 / f0 and corrects it to a spatial phase difference (Δφ0 × f1 / f0) corresponding to the frequency f1. To do. That is, the spatial phase difference is normalized by multiplying the spatial phase difference by the ratio between the ultrasonic frequencies.

  In step S14, the speckle index calculation unit 30 calculates the absolute value (| Δφ0) of the difference between the corrected spatial phase difference (Δφ0 × f1 / f0) corresponding to the frequency f1 and the spatial phase difference Δφ1 of the frequency f1. X (f1 / f0) −Δφ1 |) is calculated. In this example, the absolute value of the difference is calculated for each pixel in the phase difference image generated by the phase difference image generation unit 28.

  In step S15, the speckle index calculation unit 30 integrates the absolute value of the difference with a kernel of a predetermined size. For example, as shown in FIG. 3, integration is performed in the azimuth direction x, the distance direction y, and the slice direction z. That is, the integration is performed in the constant volume 304 of FIG. A certain area may be integrated in the azimuth direction x and the distance direction y. There is also a method of performing integration of a certain length only in the distance direction x or y.

  In step S16, when the integral value (Σ | Δφ0 × (f1 / f0) −Δφ1 |) as the speckle index is greater than or equal to the threshold value by the image processing unit 40, it is determined as speckle noise. For example, in the image, it is determined that the position of the pixel (305 in FIG. 3) located at the center of the kernel (space of a certain size) is the speckle noise position. In the real space, the reflection point denoted by reference numeral 315 of the subject 90 in FIG. 3 corresponds to the speckle noise position.

  In addition, although the case where there are two types of frequencies has been described as an example, any number of frequencies may be used. When the frequency type is N (> 2), for example, first, the spatial phase difference at the frequency f0 is corrected to be equivalent to the frequencies f1, f2, f3,..., F (N−1), and the frequency f1 , F (N−1) corresponding to the frequency f2, f3,..., F (N−1), and spatial corresponding to the frequency f3,. Thus, the spatial phase difference is corrected (corresponding to step S13). Next, the corrected spatial phase difference (f1, f2, f3,..., F (N-1)) equivalent to the corrected spatial phase difference) and each frequency (f1, f2, f3,... ..., The sum of absolute values of differences from the phase difference at f (N-1)) is calculated (corresponding to step S14).

  Further, in order to easily understand the use of the speckle index, the case of performing a binary determination as to whether it is speckle noise or a non-speckle signal in step S16 has been described. The present invention is not particularly limited when performing binary determination. Needless to say, the speckle index can also be used for multi-level determination. Further, speckle index calculation processing (e.g., corresponding to steps S11 to 15 in FIG. 6) may be incorporated during various processing without explicitly determining speckle.

  For example, in the case of speckle removal processing, as the speckle index indicating the speckle-likeness (for example, the kernel integral value of the absolute difference value) is larger, the speckle removal coefficient and range may be increased to enhance removal.

  Also, instead of the integral value of the absolute difference value, the maximum value (for example, the maximum value of the absolute difference value in the kernel) or the variance (for example, the variance of the differential value in the kernel) is used as the speckle index. It may be calculated.

  FIG. 7 shows the flow of tissue property analysis processing in the image processing unit 40.

  First, the speckle density calculation unit 372 calculates the speckle density in a certain size region with respect to the speckle index. For example, as shown in FIG. 8, the number of speckle pixels in the peripheral region Q (calculation range) including the pixel of interest P (calculation range) or the real space area (volume) is calculated, and the ratio to the entire region Q is output as the density. . In addition, the region Q may be designated by the user or may be a region according to the tissue obtained from the edge of the amplitude information or the like, and the target pixel P is not necessarily provided. Further, since the resolution of the ultrasonic echo changes depending on the depth, a density weight corresponding to the depth may be given.

  The obtained speckle density may be output as tissue property data as it is, but may be converted into tissue information associated with the density, for example, the speed of sound, and output by the tissue property conversion unit 374. In this case, for example, it is preferable to perform conversion based on reference data in which the relationship between density and tissue information is previously associated as shown in FIG.

  FIG. 10 shows an example of the display of the tissue property data.

  As shown in FIG. 10, the tissue property data may be displayed as it is superimposed on the B-mode image. Alternatively, the result of the tissue property analysis may be used for signal processing reconstruction or image quality adjustment.

  Hereinafter, examples of various uses of the tissue property analysis results will be described.

  For example, as described in the reference (GWMcLaughlin, “Practical Aberration Correction Methods,” “Ultrasound, vol.15, no.2, 2007.pp.99-104), IQ is generated from a single received data according to different sound speeds. In the case of an apparatus capable of generating data, as shown in the sound speed analysis / correction flow in FIG. 11, the average sound speed in the screen is analyzed at the first time, and the image data is generated in the image processing unit 40 for the IQ data generated at the sound speed. Try to analyze the properties.

  Here, as a method for analyzing the average sound speed, a method of comparing resolutions of images is used. For example, as described in the above-mentioned reference, it is preferable to use a method of performing comparison of power spectra of sound speeds by FFT (Fast Fourier Transform).

  Next, the sound speed data obtained by converting the tissue property analysis result is fed back to the signal processing unit, and IQ data in which the sound speed is changed again according to the value of the sound speed corresponding to the data position is generated. Since signal processing that matches the sound speed of each tissue is performed by this processing, the generated B-mode image has an image quality with resolution equal to or higher than that of the conventional method in all regions.

  In addition, when a certain average sound speed is not known as in the prior art, it is unclear how much the observed tissue differs from the sound speed assumed in the signal processing. ), The actual distance per pixel cannot be obtained, so that the required speckle density can only be determined to be relatively large or small. In this case, the speckle density for each set sound speed is required. On the other hand, when the average sound speed in the screen as in the above reference is known, the actual distance can be estimated to some extent, so the speckle density can be converted to an actual distance, so it becomes an index close to an absolute value, enabling high-precision analysis It becomes.

  Next, an example in which tissue property data is used for image quality adjustment will be described.

  When converting from amplitude information to a B-mode image, tissue information is given as a reference for image quality setting so that an appropriate luminance range is obtained depending on the tissue. For example, when adjusting the dynamic range in the mammary gland, as shown in the luminance distribution in FIG. 12, the dynamic range (DR) ). At this time, of course, not only the dynamic range but also values such as gradation, gain, and speckle removal intensity may be adjusted according to the tissue. Although the case where the speckle index is used for the tissue property analysis has been described above, the present invention is not limited to such a case. The speckle index can be used for various processes such as separation of non-speckle signals and speckle noise, removal of speckle noise, speckle tracking, and non-speckle part enhancement. Further, a speckle index may be calculated within each process.

  Recent software-based ultrasonic devices have received signals as digital data. For example, using received signals obtained from the same transmission (single transmission), RF data of two or more sound rays in the azimuth direction (reception focus) Received data) can be generated. Also, analog bases have been able to do the same with high-performance circuit configurations. With this apparatus configuration, it is possible to obtain adjacent sound ray data or frame RF data at high speed, so that the spatial phase difference can be calculated with high accuracy.

  The present invention is not limited to the examples described in the present specification and the examples illustrated in the drawings, and various design changes and improvements may be made without departing from the scope of the present invention. is there.

Explanatory drawing used to explain the positional relationship between the ultrasound probe and the subject (A) is a schematic diagram of a regular reflected wave and an interference wave constituting an ultrasonic echo, (b) is a graph showing a correspondence relationship between a frequency and a spatial phase difference in a non-speckle signal, and (c) is a speckle. Graph showing correspondence between frequency and spatial phase difference in noise Explanatory diagram used to explain how to integrate with the kernel Flow chart used to explain the outline of speckle index calculation processing The block diagram which shows the structural example of the ultrasonic image processing apparatus containing the ultrasonic signal processing apparatus which concerns on this invention The flowchart which shows the flow of the principal part of an example of the ultrasonic signal processing which concerns on this invention. Block diagram used to explain the case where speckle index is used for tissue property analysis Explanatory diagram used to explain calculation example of speckle density Table showing an example of reference data indicating the correspondence between speckle density and substance Explanatory drawing showing a display example of organizational property data Block diagram showing an example of sound velocity analysis / correction flow Diagram showing an example of luminance distribution by tissue

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Ultrasonic image processing apparatus, 12 ... Operation part, 14 ... Display part, 20 ... Ultrasonic probe, 22 ... Transmission / reception part, 24 ... Time domain signal processing part (Temporal amplitude acquisition part, Temporal phase acquisition part) ), 26... Amplitude image generation unit (spatial amplitude acquisition unit), 28... Phase difference image generation unit (spatial phase difference acquisition unit), 30... Speckle index calculation unit, 40. Part, 44 ... mode switching part

Claims (14)

An ultrasonic transmission / reception means for transmitting an ultrasonic wave toward the subject, receiving an ultrasonic echo from within the subject, and generating a reception signal indicating the ultrasonic echo;
Phase difference acquisition means for acquiring a plurality of phase differences respectively corresponding to the frequencies of the ultrasonic waves from the received signal;
Speckle index calculating means for calculating a speckle index corresponding to the magnitude of a ratio of a plurality of the frequencies and a ratio of the plurality of phase differences;
An ultrasonic signal processing apparatus comprising:   The speckle index calculating means corrects the phase difference by multiplying the phase difference by a ratio between the frequencies, and calculates the speckle index by comparing with the phase difference after correction. The ultrasonic signal processing apparatus according to claim 1.   The speckle index calculating means calculates the speckle index for each spatial position by integrating the absolute value of the phase difference after correction in a space of a fixed size including each spatial position. The ultrasonic signal processing apparatus according to claim 2.   The ultrasonic signal processing apparatus according to claim 1, wherein ultrasonic waves having different frequencies are respectively transmitted from the ultrasonic transmission / reception means.   4. The ultrasonic signal processing apparatus according to claim 1, wherein ultrasonic waves having a plurality of frequency bands are transmitted from the ultrasonic transmission / reception unit, and the received signal is divided into bands. 5.   4. The ultrasonic signal processing apparatus according to claim 1, wherein a fundamental wave is transmitted from the ultrasonic transmission / reception unit, and a fundamental wave component and a harmonic component are extracted from the received signal. 5. .   7. The speckle index calculation unit uses data whose phase resolution in the arrangement direction of the elements of the ultrasonic transmission / reception unit is equal to or greater than the interval between the elements. An ultrasonic signal processing apparatus according to 1. The ultrasonic transmission / reception means can generate the reception data of two or more sound rays in the arrangement direction of the elements of the ultrasonic transmission means in one ultrasonic transmission,
The ultrasonic according to any one of claims 1 to 7, wherein the speckle index calculation means uses the reception data of two or more sound lines generated by the ultrasonic transmission / reception means. Signal processing device. The speckle index is used to separate non-speckle signals and speckle noise, to remove speckle noise, to perform speckle tracking, to analyze tissue properties, or to perform non-speckle partial enhancement. The ultrasonic signal processing apparatus according to any one of 1 to 8.   The ultrasonic signal processing apparatus according to claim 1, wherein an image in which the speckle index is reflected is displayed on a display unit.   The image reflecting the speckle index and the amplitude image indicating the spatial amplitude of the received signal are combined and displayed on the display means. The ultrasonic signal processing apparatus described.   10. The ultrasonic signal processing apparatus according to claim 1, wherein an amplitude image indicating a spatial amplitude of the received signal is modulated by the speckle index and displayed on a display unit. .   The mode switching means for switching between a mode for displaying an image in which the speckle index is reflected and a mode for not displaying an image in which the speckle index is reflected. The ultrasonic signal processing apparatus of Claim 1.   Transmits ultrasonic waves toward the subject, receives ultrasonic echoes from within the subject, generates a reception signal indicating the ultrasonic echoes, and corresponds to the frequency of the ultrasonic waves from the received signals, respectively An ultrasonic signal processing method comprising: obtaining a plurality of phase differences, and calculating a speckle index corresponding to a magnitude of a ratio of the plurality of frequencies and a ratio of the plurality of phase differences.

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